The aim of present study was to investigate the effects of sub-lethal concentrations of silver nanoparticles (AgNP) on hematological parameters, differential tests of white blood cells, serum metabolite parameters, serum enzymes activity and serum ions in rainbow trout, Oncorhynchus mykiss. Healthy rainbow trout, were exposed to sub-lethal concentrations (0, 1.5 and 2.5 ppm) of nanosilver for 14 days. RBC, WBC and Hct levels were significantly (P<0.05) increased in exposed groups. Within the white blood cells, only neutrophils showed a significant increase at 7 and 14 days post exposure (P<0.05). Serum triglyceride, total serum protein, albumin and globulin levels were decreased (P<0.05) in exposed fish, however, cholesterol levels increased in the 2.5 ppm group at 7 days after exposure (P<0.05). Cortisol and glucose increased significantly at 7 and 14 days of exposure in both concentrations of AgNPs (P<0.05). Decreases in serum ions level were observed, although reduction in chloride ions occurred earlier and more severe than other measured parameters (P<0.05). Elevation in serum ALP, LDH, ALT and AST enzymes were observed during the experiment (P<0.05), although SOD and CAT activity were significantly decreased in exposed groups (P<0.05). The results revealed that AgNP can affect the hematological, serum metabolite and enzymatic parameters of O. mykiss, as well as AgNP exposure induce a general oxidative stress response in O. mykiss
